Gel Time Determination Research Articles

Determination of gel time of prepreg in copper clad laminate industry by near infrared spectroscopy

Gel time of prepreg is an important quality determinant in the manufacturing process of copper clad laminate (CCL). Prepreg consists of a glass fiber reinforcement impregnated to a predetermined level with a resin matrix. In this work, near infrared spectroscopy associated with partial least squares (PLS) regression has been applied to analyse the gel time of prepreg samples in the manufacturing process. A total of 250 prepreg samples were randomly divided into a calibration set and a validation prediction set with a ratio of 4:1. The values of root mean square error of leave-one-out cross-validation (RMSECV) and the coefficient of determination (R2) of the calibration model was 2.95 s and 0.92 respectively, with eight PLS factors used. The results of the paired t-test revealed that there was no significant difference between the NIR method and the reference method. The analytical result showed that, NIR spectroscopy was a rapid, nondestructive, and accurate method for real-time prediction of prepreg quality in the CCL manufacturing process.

Determination of gel time and gel point of epoxy-amine thermosets by in-situ near infrared spectroscopy

A method of near-infrared spectroscopy combined with wavelet transform was proposed to determine in-situ the gel time and gel point of epoxy resin simultaneously. The reconstructed spectra of the low-frequency wavelet coefficients were used for determination of gel time, and the reconstructed spectra of some detail coefficients which are dominated by chemical information for determination of epoxy conversion. In-situ determination of gel point has been achieved using evolutionary near infrared spectra of epoxy curing. The accuracy of gel point achived to 0.01. Compared with the traditional determination method of gel point, in which TMA and DSC are respectively used for gel time and conversion, this method not only can determine in-situ gel time and conversion degree simultaneously, and remarkably improve accuracy of the gel point result but also is of low cost, and fast and easy to operate.

Synthesis and Characterization of Interpenetrating Polymer Networks (IPNs) from Acrylated Soybean Oil and α-Resorcylic Acid: Part 1. Kinetics of Network Formation

Interpenetrating polymer networks (IPNs) using an epoxy phase synthesized from chemically modified α-resorcylic acid, and an acrylate phase employing acrylated soybean oil are the main focus of this study. Part 1 details the epoxidation of α-resorcylic acid with epichlorohydrin in alkaline medium, as well as the study of the polymerization and network formation of the generated epoxy-acrylate interpenetrated systems. The epoxy content of the epoxidized α-resorcylic acid was measured by means of a titration using HBr in acetic acid solution, and the functionalization was studied by FTIR. From the obtained results, mainly calorimetry and gel time determination, it was clear that each phase is affected by the presence of the other, altering the rate and extent at which each individual reaction takes place; and that the two noncompeting reactions (step and free radical polymerizations) occurred at very close temperatures, with a very small gap of around 10 °C between the onsets of the reactions. This evidence leads to the conclusion that the IPNs are formed by a simultaneous process in which both of the networks are formed at approximately the same temperature.

Development of Polymer Concrete with Non-Standardised Fillers for Innovative Building Materials

The use of polymer concrete in building construction is a relatively new application. A building block system (Modular Assembly System: MAS-System) and the mobile fabrication technology for the reversible construction of buildings with regionally available aggregates, were developed in a project of applied research. The aspects of the successful material development are described, especially with regard to the characterisation of both the binders and the polymer concretes, considering strength and durability. The polymer concrete consists approximately of 90 % fillers, 10 % polymer binder and additives. The investigation of the binder-system included the determination of gel time and temperature development, shrinkage, wetting of formwork materials and immersion tests with marine water. The aim was an adaptation and optimisation of the binder system. The characterisation of mechanical properties of the polymer concrete was realised by determining its strength in a temperature range between - 40 °C and 60 °C. Compression tests on wall segments were also realised. Ageing is an important aspect of the durability of polymer bonded materials. Special tests were used for an accelerated ageing, including impacts of temperature change, cold rain water and natural radiation.

Development of environmentally friendly composite matrices from epoxidized cottonseed oil

The continuous rise in oil prices has led to the use of other ways to obtain polymer materials. This paper proposes a methodology to obtain a thermosetting resin from cottonseed oil by epoxidation process. The cottonseed oil contains as most representative fatty acids: 52.5% of linoleic acid (C18: 2), 23.9% of palmitic acid (C16: 0) and 17.6% of oleic acid (C18: 1); the real iodine index, which is indicative of the number of double bonds, has a value of 107. Epoxidized cottonseed oil (ECSO) has been successfully obtained using conventional epoxidation process with hydrogen peroxide, acetic acid and sulfuric acid, maintaining a constant temperature of 70°C with homogeneous magnetic stirring. Average oxirane oxygen content (OOC) of 5.32% can be obtained by conventional epoxidation process which represents a yield over 83%. The epoxidized oil has been crosslinked with mixtures of two cyclic anhydrides to tailor different properties on final crosslinked thermosetting resins: on the one hand, methyl nadic anhydride (MNA) which is characterized by a rigid molecular structure and on the other hand, dodecenylsuccinic anhydride (DDSA) with a long side chain that can confer flexibility. The crosslinking process has been followed by dynamic differential scanning calorimetry (DSC), ionic mobility and oscillatory rheometry (OR) as well as gel time determination. The effect of the hardener mixture (wt.% DDSA:MNA) on mechanical performance of cured materials has been followed by flexural and impact tests as well as the evolution of the storage modulus (G′) by dynamic mechanical analysis (DMA) in torsion mode. By selecting the appropriate hardener mixture, it is possible to obtain crosslinked materials with different properties ranging from stiff matrices for ECSO crosslinked with MNA to flexible matrices for ECSO cured with DDSA. This has occurred with other thermosetting resins like epoxidized soy bean oil (ESBO) or epoxidized linseed oil (ELO).

An experimental study of silicate–polymer gel systems to seal shallow water flow and lost circulation zones in top hole drilling

Abstract Shallow water and lost circulation are frequently encountered problems during drilling top holes of oil and gas wells. Plenty of methods have been applied to overcome these problems. Among these methods, silicate based gels are one of the oldest. For this study, Sodium-Silicate based gel system is investigated experimentally and several aspects of the system are improved for efficient field applications. This improved gel system is deliberately delayed, multi-component system to be mixed as a uniform liquid at the surface facilities but desired to form gel structure where it is placed in the well. Gel slurries are composed of distilled water, Sodium-Silicate solution, polymer solution, lost circulation materials, weighting agent and organic initiator (initiating the gelation). In this study, effect of these components on gel time, gel quality and gel strength at room temperature is investigated as a function of their concentration. In order to compare gelation time of different compositions, a new, easy and consistent gel time determination method is developed. Being based on vortex closure time, the method can be followed easily even by basic rig laboratories. Another new method is introduced to monitor long term gelation process by measuring turbidity (NTU) of the mixtures and plotting NTU versus time curves. In addition, unique observation codes are defined to compare the gel qualities of different compositions. For gel time and quality experiments, Sodium-Silicate concentrations from 3.5% to 15% by weight in the mixture were investigated and the concentrations range of 7.5–10% were found as applicable. It is determined that, gel time is getting higher as silicate–initiator ratio (SIR) increases for these optimum concentrations. The system is improved by addition of two different polymer solutions. These polymers not only improve the elasticity of the final gels but also provide sufficient viscosity to keep weighting agent and/or lost circulation materials (LCM) in suspension. In addition, viscosity development curves obtained from rotational viscometer at various constant shear rates indicated that, gelation is accelerated by applied shear. Furthermore, HTHP filter press cell was modified by manufacturing new bottom cap with 1 mm diameter hole in center to determine the extrusion pressures of the gels and it was found that, extrusion pressure can be increased by the addition of fibrous type lost circulation materials.

A new approach for determination of gel time of a glass/epoxy prepreg

AbstractGel time of a glass/epoxy prepreg, HexPly®1454, was investigated by a parallel plate rheometer. The prepreg is based on dicyandiamide (DICY)‐cured diglycidyl ether of bisphenol A epoxy resin system. It is found that the application of the G′‐G″ crossover method for gel time determination is not suitable for this system. A new approach was proposed in which the maximum tan δ is regarded as the gel point. This can accurately define the gel point at various temperatures. The results proved that this point is independent of the applied frequency. The activation energy for the cure reaction of the system was determined via gel time determination of the prepreg at different isothermal temperatures and found to be 75.0 ± 10.2 kJ/mol. This is in good agreement with the activation energy obtained from the dynamic DSC studies. The steady‐shear rheology experiment was used to study the viscosity profile and subsequently to determine the gel point and verify the new approach for gel time determination. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Magnetic nanocomposites obtained using high evaporation rate magnetic nanofluids

In this paper, we study the influence of the addition of small amounts of nanomagnetic fluids in resins, some specific properties of these fluids and the possibility to produce a new category of magnetisable nanocomposite materials. The research was focused on the compatibility between the various types of nanomagnetic fluids and resins. Samples were prepared varying the resins, carrier liquids and volume fraction of magnetic nanoparticles. The polymerisation process of nanocomposites was investigated under the influence of applied magnetic field. Results of investigations presented in this paper refer to the microstructure of the samples (optical and/or electronic microscopy), and to the mechanical properties corresponding to different preparation methods (three points bending test, elastic properties, gel time determination).

Methacrylate/acrylate terminated derivatives of diglycidyl hexahydrophthalate: Synthesis, structural, and thermal characterization

AbstractMono‐ or di(meth)acrylate‐terminated derivatives of diglycidyl hexahydrophthalate (ER) were prepared by reacting 1 : 1 or 1 : 2M ratio of ER and methacrylic acid or acrylic acid. These vinyl ester (VE) resins were characterized by determining epoxy equivalent weight, acid number, and molecular weight by gel permeation chromatography. Structural characterization was done by FTIR and 1H NMR spectroscopy. In the 1H NMR spectra of acrylate‐terminated VE resins, three proton resonance signals were observed in the region 5.8–6.4 ppm due to vinyl group while in methacrylate‐terminated VE resins only two proton resonance signals due to vinylidene protons were observed at 5.6–6.1 ppm. The Brookfield viscosity (room temperature (25 ± 2)°C) of these resins diluted with varying amounts of MMA was determined at 20 rpm. Curing behavior was monitored by determination of gel time and differential scanning calorimetry. An exothermic transition was observed in the DSC scans in the temperature range of (81–150)°C. Isothermal curing of MMA‐diluted VE resins containing AIBN as an initiator was done at 60°C for 2 h in N2 atmosphere, and then heating for another 2 h in static air atmosphere. Thermal stability of isothermally cured resins in N2 atmosphere was evaluated by thermogravimetric analysis. All cured resins decomposed above 310°C in single step. Thermal stability of the cured resins having acrylate end caps was marginally higher than the resins having methacrylate end groups. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Use of rheology, dielectric analysis and differential scanning calorimetry for gel time determination of a thermoset

Measurements of gel time of the epoxy system DGEBA( n=0)/ m-XDA were carried out using rheometry and dielectric analysis with the objective of checking the validity of Mangion–Johari equation (DEA) and Harran–Laudouard criterium (rheometry) for gel time determination. In this work, gel times obtained by rheometry and dielectric analysis are compared and conversions at gel time calculated. From the experimental results obtained for gel times it was found a reasonable agreement between the two techniques that lead to gel conversion values very close to those obtained using Flory equation.

Cure Behaviour and Structure of Dicyanate-Epoxy Novolac Blends

The cure characteristics of bisphenol A dicyanate-novolac epoxy resin blends were investigated by gel time determination and dynamic DSC. The effects of the proportion on the structures of cured blends were investigated by FTIR. In situ FTIR was utilized to study the curing mechanism and curing kinetics. The results indicated the distinct catalytic effects of the novolac epoxy resin on the curing of bisphenol A dicyanate. Due to considerable amounts of unepoxidized phenol present in the novolac epoxy resin, the reactions between phenol and cyanate disturbed the formation of the co-reaction products. The curing reactions of the blends indicated by in situ FTIR did not follow the Bauer mechanism totally. A composite mechanism of triazine-epoxy insertion and epoxy-cyanate reaction indwells in the systems. The authors suggest that most of the oxazolidinone present in the blends is formed by isomerization of oxazoline rather than by insertion of epoxy into isocyanurate. The amount of epoxy resin in the blend did not alter the curing mechanism, but had significant effects on the kinetic behaviour.

Multifunctional epoxy resins: Synthesis and characterization

The tetrafunctional epoxy resins were prepared starting from diaminodiphenylmethane, diaminodiphenylether, and diaminobibenzyl. The obtained resins were characterized by IR and 1H-NMR spectroscopy, rheological and thermal techniques. The polymerization reaction was investigated by viscosimetry. The flow activation energy and the polymerization activation energy were evaluated from the rheological data and from the critical parameters (critical time and critical viscosity at gel point). The viscosity measurements and gel time determination showed slight differences between the synthesized resins. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2430–2436, 2000

Effect of α‐methyl styrene on properties of epoxy‐novolac based vinyl ester resins

AbstractThe paper describes the synthesis of vinyl esters using epoxy‐novolac resin. The curing behaviour of the resins containing different portions of styrene and α‐methyl styrene (α‐MS) as reactive diluents was studied by gel time determination. Delayed curing was observed in samples containing increasing proportions of α‐MS. An increase in the α‐MS content resulted in a decrease in the tensile strength and increase in heat deflection temperature of the cured sheets. The flexural strength and flexural modulus of both resin and glass fibre‐reinforced composites (resin content approx. 41 wt.‐%) increased. Treatment with boiling water (12 h) of laminates resulted in a decrease in interlaminar shear strength with an increase in α‐MS content.

Curing of epoxy resins by dicyandiamide

The reaction course, the final structure and the thermal behaviour of dicyandiamide cured epoxy resins were studied by HPLC, Carbon-13 NMR (liquid and solid state), IR, gel time determination, DSC and evolved gas analysis. N, N-dimethyl-benzylamine, imidazole and Monuron were applied as three different accelerator types. Dimethylformamide was used as solvent to obtain homogeneous reaction mixtures. Two reaction pathways depending on tautomeric dicyandiamide structures are suggested explaining the reaction mechanism.